Angiogenesis, the process whereby new blood vessels sprout and emerge from an established network, has been widely investigated in most organs. Understanding the mechanisms involved is important both for therapeutic promotion of new vessel growth in ischemic tissues as well as retardation of the process in tumors. In this proposal, we utilize a unique mouse model that allows study of the signaling of both of these processes in the lungs within individual animals. The lung is unique in that angiogenesis takes place in an ischemic but hyperoxic environment and the new vasculature is from systemic (bronchial or intercostal) arteries and not the pulmonary vasculature. After lateral thoracotomy and ligation of the left pulmonary artery in the mouse, rapid new blood vessel growth results from the intercostal arteries in immediate proximity to the site of thoracotomy. Within 5-7 days, these new blood vessels invade the upper ischemic lung region but not the lower ischemic lung. Pulmonary ischemia is essential since sham thoracotomy does not result in lung angiogenesis. These observations suggest cross communication of the thoracic wall undergoing wound repair with the upper ischemic lung. Preliminary data demonstrate that the ELR+, C-X-C chemokines in both the thoracic wall and the upper ischemic lung are essential proteins participating in this cross communication. We hypothesize that pulmonary ischemia induces lung tissue proteins that stimulate nearby intercostal vessels, to proliferate and invade the ischemic lung. Specific aims of this proposal are to determine the dynamics of chemokine synthesis in the lung and thoracic wall, with emphasis on the relative differences between the ischemic upper and lower lung regions after left pulmonary artery ligation. We will correlate the changes in chemokine expression with physiologic assessment of the magnitude and distribution of new systemic blood flow to the lung. In vitro studies assessing mouse endothelial cell proliferation and migration will be used to determine critical factors defining the proangiogenic phenotype of systemic arterial endothelial cells relative to pulmonary endothelial cells. The results of these studies will provide important new information defining the molecular, structural, and functional events of lung angiogenesis.